It is standard procedure in the manufacture of a camshaft, particular the type used in an automotive vehicle to open and close the valves of the internal-combustion engine thereof, to rough-grind the casting serving as the blank for the camshaft. Such rough-grinding is normally conducted by rotating the camshaft about its axis between centers, lathe-fashion. Meanwhile a driven grinding wheel operated off a master cam performs on the camshaft a grinding operation that gives it the basic shape at the cam and bearing surfaces. Normally several such driven grinding heads are employed at the same time on the camshaft, being driven radially against it in one direction under the guidance of the afore-mentioned master guide cams.
Subsequently the coarse-ground cam surfaces and prefinished by means of coarse prefinish tools, and then finish-ground be means of fine finish tools. These tools are normally either constituted by appropriately shaped ceramic blocks of the appropriate grit, or by synthetic-resin blocks in which the appropriate grit has been embedded. A roughness of about 0.2 microns is normally desired at the end of the prefinishing, and a roughness of about 0.1 microns is desired at the end of the fine-finishing operation.
Typically this is done simply by urging the appropriately shaped tools radially against the camshaft with a predetermined force while rotating the camshaft. The tools will smooth out the coarse-ground surfaces, which smoothing out is sometimes aided by slight axial reciprocation of the camshaft as it is rotated. First the coarse finishing operation is carried out, then the coarse finish tools are removed and the fine finish tools are urged against the cam surfaces.
It is absolutely essential that the cam surfaces be perfectly smooth and perfectly formed. The above-described procedure produces a good product. Nonetheless a more finely finished cam surface will result in substantially descreased wear and correspondingly longer engine life.